This paper aims to investigate the effect of the multi-party system on national security stability in Indonesia. There are two questions related to national defense and security aspects, namely how many political parties are suitable, and how do the election and the number of parties influences the stability of national security? The research approach is a mixed method. For quantitative methods, we use inferential statistical analysis based on statistical data from the 1955 to 2019 elections and the 2005-2018 local elections. From the Effective Number of Election Parties (ENEP), the total Crime, and the Indonesian Democratic Index, we find that all national voters in each election in Indonesia will accumulate significantly in the range of five to ten parties, regardless of the number of political parties participating in the election. For qualitative methods, we formed a two-session FGD that discussed ENEP and its risks to national defense and security and how to recommend related policies. We conclude that the 4-5% Electoral threshold is sufficient to be enforced as a rule in the next election. Local elections (pilkada) outside Java and Bali have a more significant influence on national security stability than national legislative elections. The implications of this study encourage policymakers in the field of national defense and security to take anticipatory steps towards differences in the risks of holding elections and local elections (pilkada), as well as the direction and focus of pilkada research, especially in the perspective of national defense and security.